Weather, Climate & Water Cycle

Water on Earth is never lost. It moves in a never-ending loop called the water cycle. The sun powers the cycle by warming oceans, lakes, and rivers, and lifting water into the sky. Eventually that water comes back down as rain or snow, fills the rivers and oceans again, and the cycle starts over.

The 4 Stages of the Water Cycle

1. Evaporation — heat from the sun turns liquid water from oceans, lakes, and rivers into invisible water vapor that rises into the air.
2. Condensation — high in the cooler atmosphere, the vapor cools and turns back into tiny droplets that gather to form clouds.
3. Precipitation — when droplets in clouds become too heavy, water falls back to Earth as rain, snow, sleet, or hail.
4. Collection — water gathers in oceans, lakes, rivers, and groundwater, where it can evaporate again and continue the cycle.

Weather vs Climate

Weather and climate sound similar but they describe different time spans. Weather is what is happening RIGHT NOW outside your window. Climate is the average pattern of weather a place has over many years.

• Weather changes from hour to hour and day to day — it can be sunny in the morning and rainy in the afternoon.
• Climate is measured over decades — a desert is hot and dry every year, even if today happens to be cool.
• A single rainy day does not change the climate. Many rainy years do.
• Common climate types: tropical, desert, temperate, polar.

The Sun is the Engine

Without the sun, water on Earth would simply sit still. The sun heats surface water, drives evaporation, and powers the wind that moves clouds. Every drop of rain you see was lifted into the sky by energy from the sun.

• The sun warms oceans, lakes, and rivers — water becomes vapor.
• Wind (also driven by sun-heated air) moves clouds across the sky.
• Plants release water vapor too — this is called transpiration.
• Runoff is the water that flows over land back to rivers and oceans; infiltration is the water that soaks into the soil to become groundwater.